1. Field of the Invention
This invention relates to a rotary hearth furnace having enclosed preheater means connected thereto whereby combustion gases from the rotary furnace are caused to exit the furnace and enter the preheater section to preheat the work.
2. Description of the Prior Art
Rotary hearth furnaces are known wherein an annular floor or hearth is rotated within a chamber formed by refractory material. See for example U.S. Pat. No. 1,576,371 (Seever) and 2,296,791 (Keener et al).
Moreover, induction furnaces having both preheat and combustion chambers are known wherein the higher temperature combustion chamber provides heat to a lower temperature preheat section. See U.S. Pat. No. 1,403,316 (Gaskill).
Also, two chamber rotary furnaces comprising a first stage high temperature cylinder and a second stage lower temperature cylinder are known. See U.S. Pat. No. 457,589 (De Navarro).
In heating metallic objects, certain metals have been found to crack upon being suddenly thrust into a hot hearth without having been preheated. Moreover, it is desirable for subsequent processing that the work piece be evenly heated, i.e., the inner core and external surface should be heated to substantially the same temperature.
A rotary hearth furnace differs substantially from an in-line furnace in that the entrance always involves a hot hearth. In prior practice, where a cold billet was fed to a hot hearth, excessive scaling was encountered. Also, this procedure resulted in heating the outside of the billet much more than the center. Also, productivity suffered because of the extra time needed to transfer the heat into the center of the billet.
Conservation of fuel has become increasingly important. In an in-line furnace production can be increased (as can thermal efficiency) by simply increasing the length of the furnace. However, this is very difficult to do in an existing rotary furnace, because of its inherent principle. This has been a serious problem in the art.